At a recent meeting of the Physical Society, London, Mr. James
Swinburne read a paper on alternate current condensers. It is, he
said, generally assumed that there is no difficulty in making
commercial condensers for high pressure alternating currents. The
first difficulty is insulation, for the dielectric must be very thin,
else the volume of the condenser is too great. Some dielectrics 0.2
mm. thick can be made to stand up to 8,000 volts when in small pieces,
but in complete condensers a much greater margin must be allowed.
Another difficulty arises from absorption, and whenever this occurs,
the apparent capacity is greater than the calculated. Supposing the
fibers of paper in a paper condenser to be conductors embedded in
insulating hydrocarbon, then every time the condenser is charged the
fibers have their ends at different potentials, so a current passes to
equalize them and energy is lost. This current increases the capacity.
One condenser made of paper boiled in ozokerite took an abnormally
large current and heated rapidly. At a high temperature it gave off
water, and the power wasted and current taken gradually decreased.
When a thin plate of mica is put between tin foils, it heats
excessively; and the fall of potential over the air films separating
the mica and foil is great enough to cause disruptive discharge to the
surface of the mica. There appears to be a luminous layer of minute
sparks under the foils, and there is a strong smell of ozone. In a
dielectric which heats, there may be three kinds of conduction, viz.,
metallic, when an ordinary conductor is embedded in an insulator;
disruptive, as probably occurs in the case of mica; and electrolytic,
which might occur in glass. In a transparent dielectric the conduction
must be either electrolytic or disruptive, otherwise light vibrations
would be damped. The dielectric loss in a cable may be serious.
Calculating from the waste in a condenser made of paper soaked in hot
ozokerite, the loss in one of the Deptford mains came out 7,000 watts.
Another effect observed at Deptford is a rise of pressure in the
mains. There is as yet no authoritative statement as to exactly what
happens, and it is generally assumed that the effect depends on the
relation of capacity to self-induction, and is a sort of resonator
action. This would need a large self-induction, and a small change of
speed would stop the effect. The following explanation is suggested.
When a condenser is put on a dynamo, the condenser current leads
relatively to the electromotive force, and therefore strengthens the
field magnets and increases the pressure.
[Illustration: T_{1} and T_{2} are large transformers; t_{1} and t_{2}
are small transformers or voltmeters V_{1} and V_{2}. The numbers 1,
4, 1, 25, represent their conversion ratios.]
In order to test this, the following experiment was made for the
author by Mr. W.F. Bourne. A Gramme alternator was coupled to the low
pressure coil of a transformer, and a hot wire voltmeter put across
the primary circuit. On putting a condenser on the high pressure
circuit, the voltmeter wire fused. The possibility of making an
alternator excite itself like a series machine, by putting a condenser
on it, was pointed out. Prof. Perry said it would seem possible to
obtain energy from an alternator without exciting the magnets
independently, the field being altogether due to the armature
currents. Mr. Swinburne remarked that this could be done by making the
rotating magnets a star-shaped mass of iron. Sir W. Thomson thought
Mr. Swinburne's estimate of the loss in the Deptford mains was rather
high. He himself had calculated the power spent in charging them, and
found it to be about 16 horse power, and although a considerable
fraction might be lost, it would not amount to nine-sixteenths. He was
surprised to hear that glass condensers heated, and inquired whether
this heating was due to flashes passing between the foil and the
glass. Mr. A.P. Trotter said Mr. Ferranti informed him that the
capacity of his mains was about 1/3 microfarad per mile, thus making
2-1/3 microfarads for the seven miles. The heaping up of the potential
only took place when transformers were used, and not when the dynamos
were connected direct. In the former case the increase of volts was
proportional to the length of main used, and 8,500 at Deptford gave
10,000 at London.
Mr. Blakesley described a simple method of determining the loss of
power in a condenser by the use of three electrodynamometers, one of
which has its coils separate. Of these coils, one is put in the
condenser circuit, and the other in series with a non-inductive
resistance r, shutting the condenser. If a_{2} be the reading of a
dynamometer in the shunt circuit, and a_{3} that of the divided
dynamometer, the power lost is given by r (Ca_{3} - Ba_{2}) where B and
C are the constants of the instruments on which a_{2} and a_{3} are
the respective readings. Prof. S.P. Thompson asked if Mr. Swinburne
had found any dielectric which had no absorption. So far as he was
aware, pure quartz crystal was the only substance. Prof. Forbes said
Dr. Hopkinson had found a glass which showed none. Sir William
Thomson, referring to the same subject, said that many years ago he
made some tests on glass bottles, which showed no appreciable
absorption. Sulphuric acid was used for the coatings, and he found
them to be completely discharged by an instantaneous contact of two
balls. The duration of contact would, according to some remarkable
mathematical work done by Hertz in 1882, be about 0.0004 second, and
even this short time sufficed to discharge them completely.
On the other hand, Leyden jars with tinfoil coatings showed
considerable absorption, and this he thought due to want of close
contact between the foil and the glass. To test this he suggested that
mercury coatings be tried. Mr. Kapp considered the loss of power in
condensers due to two causes: first, that due to the charge soaking
in; and second, to imperfect elasticity of the dielectric. Speaking of
the extraordinary rise of pressure on the Deptford mains, he said he
had observed similar effects with other cables. In his experiments the
sparking distance of a 14,000 volt transformer was increased from 3/16
of an inch to 1 inch by connecting the cables to its terminals. No
difference was detected between the sparking distances at the two ends
of the cable, nor was any rise of pressure observed when the cables
were joined direct on the dynamo.
In his opinion the rise was due to some kind of resonance, and would
be a maximum for some particular frequency. Mr. Mordey mentioned a
peculiar phenomenon observed in the manufacture of his alternators.
Each coil, he said, was tested to double the pressure of the completed
dynamo, but when they were all fitted together, their insulation broke
down at the same volts. The difficulty had been overcome by making the
separate coils to stand much higher pressures. Prof. Rucker called
attention to the fact that dielectrics alter in volume under electric
stress, and said that if the material was imperfectly elastic, some
loss would result. The president said that, as some doubt existed as
to what Mr. Ferranti had actually observed, he would illustrate the
arrangements by a diagram. Speaking of condensers, he said he had
recently tried lead plates in water to get large capacities, but so
far had not been successful.
Mr. Swinburne, in replying, said he had not made a perfect condenser
yet, for, although he had some which did not heat much, they made a
great noise. He did not see how the rise of pressure observed by Mr.
Ferranti and Mr. Kapp could be due to resonance. Mr. Kapp's experiment
was not conclusive, for the length of spark is not an accurate measure
of electromotive force. As regards Mr. Mordey's observation, he
thought the action explicable on the theory of the leading condenser
current acting on the field magnets. The same explanation is also
applicable to the Deptford case, for when the dynamo is direct on, the
condenser current is about 10 amperes, and this exerts only a small
influence on the strongly magnetized magnets. When transformers are
used, the field magnets are weak, while the condenser current rises
to 40 amperes. Mr. Blakesley's method of determining losses was, he
said, inapplicable except where the currents were sine functions of
the time; and consequently could not be used to determine loss due to
hysteresis in iron, or in a transparent dielectric.--_Nature._
* * * * *
THE TELEGRAPHIC COMMUNICATION BETWEEN GREAT BRITAIN, EUROPE, AMERICA,
AND THE EAST.
By GEORGE WALTER NIVEN.
There are at present twenty-six submarine cable companies, the
combined capital of which is about forty million pounds sterling.
Their revenue, including subsidies, amounts to 3,204,060£.; and their
reserves and sinking funds to 3,610,000£.; and their dividends are
from one to 14¾ per cent. The receipts from the Atlantic cables alone
amount to about 800,000£. annually.
The number of cables laid down throughout the world is 1,045, of which
798 belong to governments and 247 to private companies. The total
length of those cables is 120,070 nautical miles, of which 107,546 are
owned by private telegraph companies, nearly all British; the
remainder, or 12,524 miles, are owned by governments.
[Illustration: MAP SHOWING CABLES FROM GREAT BRITAIN TO AMERICA AND
THE CONTINENT.]
The largest telegraphic organization in the world is that of the
Eastern Telegraphic Company, with seventy cables, of a total length of
21,859 nautical miles. The second largest is the Eastern Extension,
Australasia and China Telegraph Company, with twenty-two cables, of a
total length of 12,958 nautical miles. The Eastern Company work all
the cables on the way to Bombay, and the Eastern Extension Company
from Madras eastward. The cables landing in Japan, however, are owned
by a Danish company, the Great Northern. The English station of the
Eastern Company is at Porthcurno, Cornwall, and through it pass most
of the messages for Spain, Portugal, Egypt, India, China, Japan, and
Australia.
The third largest cable company is the Anglo-American Telegraph
Company, with thirteen cables, of a total length of 10,196 miles.
The British government has one hundred and three cables around our
shores, of a total length of 1,489 miles. If we include India and the
colonies, the British empire owns altogether two hundred and sixteen
cables of a total length of 3,811 miles.
The longest government cable in British waters is that from Sinclair
Bay, Wick, to Sandwick Bay, Shetland, of the length of 122 miles, and
laid in 1885. The shortest being four cables across the Gloucester and
Sharpness Canal, at the latter place, and each less than 300 ft. in
length.
Of government cables the greatest number is owned by Norway, with two
hundred and thirty-six, averaging, however, less than a mile each in
length.
The greatest mileage is owned by the government of France with 3,269
miles, of the total length of fifty-one cables.
The next being British India with 1,714 miles, and eighty-nine cables;
and Germany third with 1,570 miles and forty-three cables.
Britain being fourth with ninety miles less. The oldest cable still
in use is the one that was first laid, that namely from Dover to
Calais. It dates from 1851.
The two next oldest cables in use being those respectively from
Ramsgate to Ostend, and St. Petersburg to Cronstadt, and both laid
down in 1853.
Several unsuccessful attempts were made to connect England and Ireland
by means of a cable between Holyhead and Howth; but communication
between the two countries was finally effected in 1853, when a cable
was successfully laid between Portpatrick and Donaghadee (31).
As showing one of the dangers to which cables laid in comparatively
shallow waters are exposed, we may relate the curious accident that
befell the Portpatrick cable in 1873. During a severe storm in that
year the Port Glasgow ship Marseilles capsized in the vicinity of
Portpatrick, the anchor fell out and caught on to the telegraph cable,
which, however, gave way. The ship was afterward captured and towed
into Rothesay Bay, in an inverted position, by a Greenock tug, when
part of the cable was found entangled about the anchor.
The smallest private companies are the Indo-European Telegraph
Company, with two cables in the Crimea, of a total length of fourteen
and a half miles; and the River Plate Telegraph Company, with one
cable from Montevideo to Buenos Ayres, thirty-two miles long.
The smallest government telegraph organization is that of New
Caledonia, with its one solitary cable one mile long.
We will now proceed to give a few particulars regarding the companies
having cables from Europe to America.
The most important company is the Anglo-American Telegraph Company,
whose history is inseparably connected with that of the trials and
struggles of the pioneers of cable laying.
Its history begins in 1851 when Tebets, an American, and Gisborne, an
English engineer, formed the Electric Telegraph Company of
Newfoundland, and laid down twelve miles of cable between Cape Breton
and Nova Scotia. This company was shortly afterward dissolved, and its
property transferred to the Telegraphic Company of New York,
Newfoundland and London, founded by Cyrus W. Field, and who in 1854
obtained an extension of the monopoly from the government to lay
cables.
A cable, eighty-five miles long, was laid between Cape Breton and
Newfoundland (22).
Field then came to England and floated an English company, which
amalgamated with the American one under the title of the Atlantic
Telegraph Company.
The story of the laying of the Atlantic cables of 1857 and 1865, their
success and failures, has often been told, so we need not go into any
details. It may be noted, however, that communication was first
established between Valentia and Newfoundland on August 5. 1858, but
the cable ceased to transmit signals on September 1, following.
During that period, ninety-seven messages had been sent from Valentia,
and two hundred and sixty-nine from Newfoundland. At the present time,
the ten Atlantic cables now convey about ten thousand messages daily
between the two continents. The losses attending the laying of the
1865 cable resulted in the financial ruin of the Atlantic company and
its amalgamation with the Anglo-American. In 1866 the Great Eastern
successfully laid the first cable for the new company, and with the
assistance of other vessels succeeded in picking up the broken end of
the 1865 cable and completing its connection with Newfoundland.
[Illustration: MAP SHOWING MAIN CABLES FROM EUROPE AND THEIR
CONNECTIONS WITH CANADA AND THE UNITED STATES.
Reference to places--A, Heart's Content; B, Placentia; C, St. Peter
Miquelon; D, North Sydney, Cape Breton Island; E, Louisbourg; F Canso,
Nova Scotia; G, Halifax; H, Bird Rock; I, Madeline Isles; J,
Anticosti; K, Charlotte Town, Prince Edward's Island; LLL, Banks of
Newfoundland.]
The three cables of this company presently in use and connecting
Valentia in Ireland with Heart's Content in Newfoundland, were laid in
1873, 1874, and 1880; and (1) are respectively 1886, 1846, and 1890
nautical miles in length. This company also owns the longest cable in
the world, that namely from Brest in France to St. Pierre Miquelon,
one of a small group of islands off the south coast of Newfoundland
and which, strange to say, still belongs to France (6).
The length of this cable is 2,685 nautical miles, or 3,092 statute
miles. It was laid in 1869. There are seven cables of a total length
of 1773 miles, connecting Heart's Content, Placentia Bay and St.
Pierre, with North Sydney, Nova Scotia, and Duxbury, near Boston,
belonging to the American company. Communication is maintained with
Germany and the rest of the Continent by means of a cable from
Valentia to Emden 846 miles long (7); and a cable from Brest to
Salcombe, Devon, connects the St. Pierre and Brest cable with the
London office of the company (10).[1]
[Footnote 1: Cables not fully described in the text, Map B. Eight
cables at the Anglo-American Company: 7, Heart's Content to Placentia,
two cables; 8, Placentia to St. Pierre; 9, St. Pierre to North Sydney;
10, Placentia to North Sydney, two cables; 11, St. Pierre to Duxbury;
18, Charlotte's Town to Nova Scotia; 19, Government Cable, North
Sydney to Bird Rock, Madeline Isles, and Anticosti; 21, Halifax and
Bermuda Cable Company's proposed cable to Bermuda.]
The station of the Direct United States Cable Company is situated at
Ballinskelligs Bay, Ireland (2). Its cable was laid in 1874-5, and is
2,565 miles in length. The terminal point on the other side of the
Atlantic is at Halifax, Nova Scotia, from whence the cable is
continued to Rye Beach, New Hampshire, a distance of 536 miles, and
thence by a land line of 500 miles to New York (17).
The Commercial Cable Company's station in Ireland is at Waterville, a
short distance from Ballinskelligs (3). It owns two cables laid in
1885; the northern cable being 2,350, and the southern 2,388 miles
long. They terminate in America at Canso, Nova Scotia. From Canso a
cable is laid to Rockfort, about thirty miles south of Boston, Mass.,
a distance of 518 miles (16), and another is laid to New York, 840
miles in length (15). This company has direct communication with the
Continent by means of a cable from Waterville to Havre of 510 miles
(9), and with England by a cable to Weston-super-Mare, near Bristol,
of 328 miles (8).
The Western Union Telegraph Company (the lessees of the lines of the
American Telegraph and Cable Company) has two cables from Sennen Cove,
Land's End, to Canso, Nova Scotia (4). The cable of 1881 is 2,531 and
that of 1882 is 2,576 miles in length. Two cables were laid November,
1889, between Canso and New York (14).
The Compagnie Française du Telegraphe de Paris à New York has a cable
from Brest to St. Pierre Miquelon of 2,242 miles in length (5), from
thence a cable is laid to Louisbourg, Cape Breton (12), and another
to Cape Cod (13). It has also a cable from Brest to Porcella Cove,
Cornwall (11).
Those ten cables owned by the six companies named, of the total milage
of 22,959, not counting connections, represent the entire direct
communication between the continents of Europe and North America.
A new company, not included in the preceding statistics, proposes to
lay a cable from Westport, Ireland, to some point in the Straits of
Belle Isle on the Labrador coast (Map A32, Map B20).
The station of the Eastern Telegraph Company is at Porthcurno Cove,
Penzance, from whence it has two cables to Lisbon, one laid in 1880,
850 miles long, the other laid in 1887, 892 miles long (12), and one
cable to Vigo, Spain, laid in 1873, 622 miles long (13). From Lisbon
the cable is continued to Gibraltar and the East, whither we need not
follow it, our intention being to confine ourselves entirely to a
brief account of those cables communicating directly with Europe and
America. As already stated, this company has altogether seventy
cables, of a total length of nearly 22,000 miles.
The Direct Spanish Telegraph Company has a cable, laid in 1884, from
Kennach Cove, Cornwall, to Bilbao, Spain, 486 miles in length (14).
Coming now to shorter cables connecting Britain with the Continent, we
have those of the Great Northern Telegraph Company, namely, Peterhead
to Ekersund, Norway, 267 miles (15). Newbiggin, near Newcastle, to
Arendal, Norway, 424 miles, and thence to Marstrand, Sweden, 98 miles.
Two cables from the same place in England to Denmark (Hirstals and
Sondervig) of 420 and 337 miles respectively (17 and 18).
The great Northern Company has altogether twenty-two cables, of a
total length of 6,110 miles. The line from Newcastle, is worked direct
to Nylstud, in Russia--a distance of 890 miles--by means of a "relay"
or "repeater," at Gothenburg. The relay is the apparatus at which the
Newcastle current terminates, but in ending there it itself starts a
fresh current on to Russia.
The other continental connections belong to the government, and are as
follows: two cables to Germany, Lowestoft to Norderney, 232 miles, and
to Emden, 226 miles (19 and 20).
Two cables to Holland: Lowestoft to Zandvoort, laid in 1858 (21), and
from Benacre, Kessingland, to Zandvoort (22).
Two cables to Belgium: Ramsgate to Ostend (23), and Dover to Furness
(24).
Four cables to France: Dover to Calais, laid in 1851 (25), and to
Boulogne (26), laid in 1859; Beachy Head to Dieppe (27), and to Havre
(28).
There is a cable from the Dorset coast to Alderney and Guernsey, and
from the Devon coast to Guernsey, Jersey, and Coutances, France (29
and 30).
A word now as to the instruments used for the transmission of
messages. Those for cables are of two kinds, the mirror galvanometer
and the siphon recorder, both the product of Sir Wm. Thomson's great
inventive genius.
When the Calais-Dover and other short cables were first worked, it was
found that the ordinary needle instrument in use on land lines was not
sufficiently sensitive to be affected trustworthily by the ordinary
current it was possible to send through a cable. Either the current
must be increased in strength or the instruments used must be more
sensitive. The latter alternative was chosen, and the mirror
galvanometer was the result.
The principle on which this instrument works may be briefly described
thus: the transmitted current of electricity causes the deflection of
a small magnet, to which is attached a mirror about three-eighths of
an inch in diameter, a beam of light is reflected from a properly
arranged lamp, by the mirror, on to a paper scale. The dots and dashes
of the Morse code are indicated by the motions of the spot of light to
the right and left respectively of the center of the scale.
The mirror galvanometer is now almost entirely superseded by the
siphon recorder. This is a somewhat complicated apparatus, with the
details of which we need not trouble our readers. Suffice it for us to
explain that a suspended coil is made to communicate its motions, by
means of fine silk fibers, to a very fine glass siphon, one end of
which dips into an insulated metallic vessel containing ink, while the
other extremity rests, when no current is passing, just over the
center of a paper ribbon. When the instrument is in use the ink is
driven out of the siphon in small drops by means of an electrical
arrangement, and the ribbon underneath is at the same time caused to
pass underneath its point by means of clockwork.
If a current be now sent through the line, the siphon will move above
or below the central line, thus giving a permanent record of the
message, which the mirror instrument does not. The waves written by
the siphon above the central line corresponding to the dots of the
Morse code, and the waves underneath corresponding to the dashes.
The cost of the transmission of a cablegram varies from one shilling
per word, the rate to New York and east of the Mississippi, to ten
shillings and seven pence per word, the rate to New Zealand. In order
to minimize that cost as much as possible, the use of codes, whereby
one word is made to do duty for a lengthy phrase, is much resorted to.
Of course those code messages form a series of words having no
apparent relation to each other, but occasionally queer sentences
result from the chance grouping of the code words. Thus a certain tea
firm was once astonished to receive from its agent abroad the
startling code message--"Unboiled babies detested"!
Suppose we now follow the adventures of a few cablegrams in their
travels over the world.
A message to India from London by the cable route requires to be
transmitted eight times at the following places: Porthcurno
(Cornwall), Lisbon, Gibraltar, Malta, Alexandria, Suez, Aden, Bombay.
A message to Australia has thirteen stoppages; the route taken beyond
Bombay being via Madras, Penang, Singapore, Banjoewangie and Port
Darwin (North Australia); or from Banjoewangie to Roebuck Bay (Western
Australia).
To India by the Indo-European land lines, messages go through Emden,
Warsaw, Odessa, Kertch, Tiflis, Teheran, Bushire (Persian Gulf), Jask
and Kurrachee, but only stop twice between London and Teheran--namely,
at Emden and Odessa.
Messages from London to New York are transmitted only twice--at the
Irish or Cornwall stations, and at the stations in Canada. Owing to
the great competition for the American traffic, the service between
London, Liverpool, and Glasgow and New York is said to be much
superior to that between any two towns in Britain. The cables are
extensively used by stock brokers, and it is a common occurrence for
one to send a message and receive a reply within five minutes.
During breakages in cables messages have sometimes to take very
circuitous routes. For instance, during the two days, three years ago,
that a tremendous storm committed such havoc among the telegraph wires
around London, cutting off all communication with the lines connected
with the Channel cables at Dover, Lowestoft, etc., it was of common
occurrence for London merchants to communicate with Paris through New
York. The cablegram leaving London going north to Holyhead and
Ireland, across the Atlantic to New York and back _via_ St. Pierre to
Brest and thence on to Paris, a total distance of about seven thousand
miles.
Three years ago, when the great blizzard cut off all communication
between New York and Boston, messages were accepted in New York, sent
to this country, and thence back to Boston.
Some time ago the cables between Madeira and St. Vincent were out of
order, cutting off communication by the direct route to Brazil, and a
message to reach Rio Janeiro had to pass through Ireland, Canada,
United States, to Galveston, thence to Vera Cruz, Guatemala,
Nicaragua, Panama, Ecuador, Peru, Chili; from Valparaiso across the
Andes, through the Argentine Republic to Buenos Ayres, and thence by
East Coast cables to Rio Janeiro, the message having traversed a
distance of about twelve thousand miles and having passed through
twenty-four cables and some very long land lines, instead of passing,
had it been possible to have sent it by the direct route, over one
short land line and six cables, in all under six thousand miles.
Perhaps some of our readers may remember having read in the newspapers
of the result of last year's Derby having been sent from Epsom to New
York in fifteen seconds, and may be interested to know how it was
done. A wire was laid from near the winning post on the race course to
the cable company's office in London, and an operator was at the
instrument ready to signal the two or three letters previously
arranged upon for each horse immediately the winner had passed the
post. When the race began, the cable company suspended work on all the
lines from London to New York and kept operators at the Irish and Nova
Scotian stations ready to transmit the letters representing the
winning horse immediately, and without having the message written out
in the usual way. When the race was finished, the operator at Epsom at
once sent the letters representing the winner, and before he had
finished the third letter, the operator in London had started the
first one to Ireland. The clerk in Ireland immediately on bearing the
first signal from London passed it on to Nova Scotia, from whence it
was again passed on to New York. The result being that the name of the
winner was actually known in New York before the horses had pulled up
after passing the judge. It seems almost incredible that such
information could be transmitted such a great distance in fifteen
seconds, but when we get behind the scenes and see exactly how it is
accomplished, and see how the labor and time of signaling can be
economized, we can easily realize the fact.
The humors of telegraphic mistakes have often been described; we will
conclude by giving only one example. A St. Louis merchant had gone to
New York on business, and while there received a telegram from the
family doctor, which ran: "Your wife has had a child, if we can keep
her from having another to-night, all will be well." As the little
stranger had not been expected, further inquiry was made and elicited
the fact that his wife had simply had a "chill"! This important
difference having been caused simply by the omission of a single dot.
-.-. .... .. .-.. .-..
c h i l l = chill
-.-. .... .. .-.. -..
c h i l d = child
--_Hardwicke's Science-Gossip_.
* * * * *